After Cuba’s revolution in 1959, Havana squandered what was arguably its best opportunity to force the United States to abandon its lease of a naval base at Guantanamo: a legal doctrine that allows a nation to terminate a treaty if a fundamental change occurs in the circumstances that led to it.

To at least some international lawyers, the revolution met the “fundamental change” standard. Cuba recognized the possibility, too, and considered this option as a way to declare the U.S. lease void. But Cuba was indecisive, and as late as 1970 it was weighing four different and partly conflicting legal arguments for ejecting the U.S. Navy from Cuban territory. In the end, it never launched a case.

Looking over Cuba’s shoulder at the time was the Soviet Union. So it is no surprise that the abrupt change of power in Ukraine made Moscow want to do something to ensure that Kiev wouldn’t try to remove Russia from the naval base it maintains at Sevastopol under a similar lease.

Russia had reason to be concerned. When the now-ousted government of Viktor Yanukovych took office in 2010, its first order of business was to have Ukrainian legislators approve a bill that was so contentious it led to fistfights in Parliament: renewing the Sevastopol lease. The bill passed.

The government that preceded Yanukovych’s had repeatedly warned that the lease wouldn’t be renewed upon its expiration in 2017. That had put Russia in a bind because its work to develop an alternate naval base at Novorissiysk, on its own territory, was moving too slowly. Moreover, that site was at the Black Sea’s eastern extremity, making it strategically inferior for projecting Russian power in the region.

The Sevastopol base is not only a leased zone but also a comfort zone for Russia in terms of food security. In years with poor crops, it has relied on Ukrainian grain to feed its population. The intimidation potential arising from the simple presence of its navy at Sevastopol likely made it more palatable for Russia to depend on a state that was legally and functionally independent from it.

Ivan Sekretarev &#x2022; Associated Press

A Ukrainian soldier guards the naval base headquarters in Novoozerne, about 60 miles west of the Crimean capital of Simferopol, Ukraine. The isolated town is torn between Ukrainians refusing to surrender their weapons and the Russian forces who arrived over the weekend.

With Kiev’s power change, Moscow could easily expect the new government, either now or after elections, to act more decisively than Cuba’s did. Even just calling for the lease to be ended would be a no-brainer for Ukrainian politicians seeking to shore up domestic political support among much of the voting population.

Russia thus finds itself in the same position as the United States did at Guantanamo half a century ago: the unwanted tenant of a hostile landlord. But it, too, has a legal principle on its side: the one that obliges a nation to honor the agreements it enters into.

A U.S. State Department lawyer put it this way in February 1962: “A declaration by Cuba that it denounced, repudiated or abrogated the Guantanamo base arrangements would be legally ineffective. Those arrangements are to continue, according to their terms, until agreed otherwise between the United States and Cuba. An allegation of the doctrine of rebus sic stantibus (changed circumstances) as a ground for unilateral termination would not be well founded.”

At what point this can be overridden by the “fundamental change” doctrine is an open question. The bar has been set high, and with Guantanamo the United States came down on the side that Russia has taken.

This gives Moscow and Washington a piece of common ground in situations that are otherwise quite different. It’s a small one, but it’s the kind of thing one looks for as an entry point into negotiations that can then be expanded outward. If there is to be a diplomatic solution to the crisis in Crimea, it may be a place to start.

Michael J. Strauss, professor at the Center for Diplomatic and Strategic Studies in Paris, is the author of “The Leasing of Guantanamo Bay” (Praeger, 2009). A University of Minnesota graduate, he is an adviser for the Guantanamo Public Memory Project display that is currently at the Minnesota History Center.